Computerized sewing apparatus was introduced more than a decade ago. Conventional systems perform sewing operations along a predetermined path using a sewing program. The main drawback of such systems lies in the fact that these systems are blind, i.e., they cannot see the work piece which is being sewn. This blindness is a severe handicap for present generation sewing systems. Leather and textiles are flexible materials which can change their size and position before and during the sewing operation. Hence, occasionally, the predetermined sewing path does not match the actual piece being sewn, and the pieces must be disqualified and rejected by quality inspectors.
A further drawback rests in the fact that, in an attempt to maintain accurate positioning of the pieces to be sewn relative to the sewing head, the sewn pieces are firmly held in a complicated workholder. This workholder aims to avoid, with limited success, the potential inaccuracy of pieces placement. Furthermore, the placement of the pieces in this workholder is complicated and, therefore, today is done manually by a trained operator.
There is disclosed in U.S. Pat. No. 4,498,404 automatic sewing apparatus including a manipulator for manipulating the workpiece on a sewing table, the manipulator head and table being designed for selectively applying either positive or negative fluid pressure in order to selectively produce either suction for holding the workpiece, or an air cushion for facilitating movement of the workpiece by the manipulator. The apparatus also includes a workpiece detector continuously monitoring the location of the edge of the workpiece with respect to the sewing head.
The sewing apparatus in U.S. Pat. No. 4,498,404 is a conventional device permitting sewing in one direction only. That is, the workpiece must be manipulated so as to always be presented to the needle from the same side of the sewing head. When a corner is reached necessitating a change in sewing direction, the apparatus stops, the workpiece is rotated through the appropriate angle, and sewing commences again with movement in the original direction. The edge detector provided is a stationary line scan camera of photo-diodes located and oriented so as to monitor the edge of the workpiece relative to a line perpendicular to the direction of sewing.
With the advent of computerized sewing systems, the limitations of uni-directional sewing were felt and systems have been developed permitting multi-directional sewing. In other words, the material to be sewn can approach the needle from any direction. This results in a tremendous time saving when sewing patterns including corners and curves, since the workpiece can be moved in the desired direction without stopping the apparatus. In such a system, however, an edge detector such as shown in U.S. Pat. No. 4,498,404 would be ineffective due to the constantly changing direction of sewing.
Furthermore, there is no discussion in U.S. Pat. No. 4,498,404 of illumination conditions or set up. It is known in the art that without appropriate illumination, no image analysis can be performed effectively. Accordingly, the disclosure with regard to edge detection is this patent is limited in scope.